Paramedics from Yorkshire Ambulance Service were called to the scene in Pearson Park shortly after 7.41pm.
They found a man in his 20s had landed on a spike, injuring his upper leg.
A spokeswoman said the man was taken to Hull Royal Infirmary for further treatment.
Crews from Humberside Fire and Rescue Service were also called out as the man was stuck behind a lock gate when paramedics first arrived.
However, access was gained soon after and the man had been released by the time they reached the scene.